Triads

Skip every other white key from C (C, E, G) and you have played a triad, the three-note chord under most of the songs you know.

Three notes stacked in thirds

A chord is three or more different notes sounding together. The most common chord in Western music is the triad, three notes stacked in thirds. Start on any note, skip a letter, take the next one, skip again, take the next: C, E, G or D, F, A or G, B, D. On the staff a triad stacked this way sits on three neighbouring lines or three neighbouring spaces, and Open Music Theory compares the shape to a snowperson with a bottom, middle and head.

Each note has a name that tells you its place in the stack. The bottom note is the root, and the chord is named after it: C, E, G is a C chord. The middle note is the third, a third above the root. The top note is the fifth, a fifth above the root. These names stick to the notes even when the chord is rearranged, so in a C chord E is always the third and G the fifth, wherever they are played.

Spelling a triad

To spell a triad on any root, first write the letters: root, skip, third, skip, fifth. D gives D, F, A. Then think of the major key signature of the root and apply only the accidentals that touch those letters. D major has F♯ and C♯; the triad uses F but not C, so the D major triad is D, F♯, A. For A♭, the letters are A, C, E, and A♭ major's signature flattens A and E, which gives A♭, C, E♭. This method always gives a major triad first; the next unit shows how to change it into the other qualities.

Doubling and spacing do not change a chord's name. A guitarist strumming six strings on an open C chord plays C, E, G, C, E (one string is silent), with C and E doubled. A pianist might play C in the left hand and E, G, C spread across the right. Both are still a C major triad, because the set of letter names is the same. To identify a spread-out chord, gather its notes into the tightest stack of thirds you can and read the bottom note.

Chord symbols, the letters printed above songs and guitar parts, name a triad by its root and quality. A capital letter alone means major: C is a C major triad. A small "m" (Open Music Theory writes "mi") marks minor, so Am is A, C, E. You will meet the symbols for diminished and augmented in the next unit. On the keyboard below, play C, E and G one at a time and then together, and compare the sound with D, F, A.